Forty cases of placental abruption were diagnosed by sonography after 20 weeks' gestation and managed expectantly. Tocolytics were used in 18 patients and were successful in delaying delivery for 34 +/- 24 days in 10. One-third of the patients delivered at term, after delays of 12.3 +/- 5.7 weeks. The majority of the patients who delivered before term (63%) had at least one other risk factor for preterm delivery, such as twins, ruptured membranes, or cervical dilation at presentation. Preterm delivery was not correlated with any of several clinical indicators of the severity of the abruption. Although the perinatal mortality rate was 22%, all perinatal deaths except one were attributable to extreme prematurity. It concluded that mild placental abruption is often a self-limited event and can safely be managed expectantly. Most of the perinatal morbidity and mortality is associated with premature delivery and, thus, in the absence of fetal distress or maternal compromise, delivery may often be delayed until fetal maturity is attained.